E-Flora BC: Electronic Atlas of the Flora of British Columbia

Polygonum douglasii Greene
Douglas's knotweed
Polygonaceae (Buckwheat family)

Introduction to Vascular Plants

© Jamie Fenneman  Email the photographer   (Photo ID #10175)

E-Flora BC Static Map
Distribution of Polygonum douglasii
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Polygonum douglasii is a native wetland species that is found across much of Canada (AB, BC, MB, ON, QC, SK) and the US (AZ, CA, CO, IA, ID, MD, ME, MI, MN, MT, ND, NE, NH, NM, NV, NY, OR, SD, UT, VT, WA, WY) (USDA 2010).

In the Illustrated Flora of British Columbia, several subspecies of P. douglasii were recognized. However, the nomenclature for this species has changed. The BC Conservation Data Centre, which determines the official list of BC plants, says: "In 2007, we decided to follow Flora North America (FNA) volume 5 which treats P. douglasii in the narrow sense and elevated the following subspecies as distinct species: ssp. austiniae, ssp. majus, ssp.nuttallii, ssp. engelmannii and ssp. spergulariiforme. This differs from how Kartesz (1999) treats P. douglasii ssp. douglasii in that FNA attributes P. douglasii ssp. johnstonii to P. sawatchense ssp. oblivium. Kartesz 1999 maintains subspecies johnstonii in P. douglasii." (Marta Donovan, personal communication, 2010).

Species Information

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Annual herb from a small taproot; stems ascending to erect, numerous, simple to freely branched, 10-40 cm tall.
Basal leaves lacking; stem leaves alternate, linear to narrowly oblong, egg-shaped or elliptic, the blades 1-8 cm long, unstalked or nearly so, sometimes reduced to bracts above; stipules short-sheathing, 5-12 mm long, clear, becoming ragged.
Inflorescence of few flowers in elongate axillary racemes; perianths 1.5-5 mm long, greenish with white or pinkish margins, 5-lobed nearly to the base.
Achenes, lanceolate to egg-shaped, sometimes 3-angled, black, smooth and shiny, 2-4 mm long.

Source: The Illustrated Flora of British Columbia

Habitat / Range

Moist to dry rocky slopes and disturbed sites in the lowland and montane zones; frequent in SC BC and on Vancouver Island, rare elsewhere in BC; E to PQ and S to NY, UT, NM and CA.

Source: The Illustrated Flora of British Columbia


Ecological Framework for Polygonum douglasii

The table below shows the species-specific information calculated from
original data (BEC database) provided by the BC Ministry of Forests and Range.
(Updated August, 2013)

Site Information
Value / Class




Elevation (metres) 304 1120 2013
Slope Gradient (%) 0 39 360
Aspect (degrees)
[0 - N; 90 - E; 180 - S; 270 - W]
0 197 360
Soil Moisture Regime (SMR)
[0 - very xeric; 4 - mesic;
8 - hydric]
0 1 6
Modal Nutrient Regime
Number of field plots
 species was recorded in:
Modal BEC Zone Class
All BEC Zones (# of stations/zone) species was recorded in: AT(7), BG(46), CWH(1), ESSF(50), ICH(25), IDF(73), MS(57), PP(31), SBPS(1), SBS(10)


The climate type for this species, as reported in the: "British Columbia plant species codes and selected attributes. Version 6 Database" (Meidinger et al. 2008), is not evaluated, unknown or variable.

Synonyms and Alternate Names

Polygonum douglasii var. austiniae (Greene) M.E. Jones

Taxonomic and Nomenclatural Links

Additional Photo Sources

General References